Preparation And Performance Of New Gel Polymer Electrolytes For Lithium-sulfur Batteries

Lithium-sulfur(Li-S)battery has become a promising candidate for advanced energy storage system owing to its low cost,environmentally friendliness and high theoretical specific energy.However,in organic liquid electrolyte(LE),the shuttling effect caused by polysulfides will severely undermine its cycling performance.And developing solid polymer electrolyte(SPE)completely eliminate the dissolution of polysulfides and significantly avoid the leakage of liquid components,but there still exist defects like low ionic conductivity at room temperature and poor stability at the electrolyte/electrode interface in SPE.Gel polymer electrolyte(GPE),combining the advantages of both LE and SPE,expected to be an attracting strategy to overcome these technical obstacles.In this thesis,to enhance mechanical strength,ionic conductivity and cycling performance of GPE,polyvinyl alcohol-based gel polymer electrolytes with excellent comprehensive properties are prepared through graft modification and electrospun technology on the basis of structural optimization and functional doping.Firstly,a bifunctional polyvinyl alcohol was synthesized via free-radical polymerization based on polyvinyl alcohol rich in hydroxyl groups with pendant nitrile-imidazole ionic liquid(ILCN)and poly(ethylene oxide)(PEO)which can promote Li+transfer.And the bifunctional polymer was blended with glyoxal cross-linker,incured by heating and cross-linking to obtain PVA-PIN polymer.Subsequently,electrospun PVA-PIN host with polyporous crosslinking network was immersed into 1 M lithium bis(triflu-oromethane)(LiTFSI)in DME/DOL(1:1 in volume)(1 M LiTFSI-DME/DOL)to prepare PAN-PIN gel electrolyte.When added PVA was 2 g,PEO was 4 mL and the content of ILCN(wt%PVA)was 10%,three kinds of materials worked and were compatible with each other.Besides,the electrolyte uptake of gel electrolyte reached 359%and the room temperature ionic conductivity was as high as 8.31 ×10-4 S cm-1,which indicated that the pendant groups played an important role in enhancing ionic transport.Li-S battery based on this GPE presented a superior cycling life with an initial capacity of 856 mAh g-1 at 0.2 C and the capacity retention maintained 75.9%after 100 circles.Secondly,in order to further improve mechanical strength and cycling performance of polyvinyl alcohol-based GPE,a composite gel electrolyte(PVA-PIN@SiO2-PYTFSI)was prepared by incorporating pyridine tethered silica nanoparticles fillers into PVA-PIN host via electrospun technology.The modified PVA-PIN@SiO2-PYTFSI fiber was rough with many small protrusions,which was beneficial to the promotion of electrolyte uptake and Li+transport,which can further enhance ionic conductivity up to 9.72×10-4 S cm-1.When applied to Li-S battery,pyridinium N in SiO2-PYTFSI could bond with lithium of polysulfides to alleviate shuttling effect and the assembled battery exhibited better cycling performance with higher initial capacity of 1043 mAh g-1 at 0.2 C and enhanced capacity retention of 84.0%.